The present invention relates to a semiconductor device, a battery monitoring system, and a method of monitoring a battery. In particular, the present invention relates to a semiconductor device including a temperature measurement circuit for monitoring a battery, a battery monitoring system using the semiconductor device, and a method of monitoring a battery using the semiconductor device.
In recent years, a conventional semiconductor device having a temperature measurement circuit has been used in a wide range of applications. Such a conventional semiconductor device includes a battery monitoring IC (Integrated Circuit). The battery monitoring IC is configured to monitor a voltage and the like generated in a charging device of a secondary battery as well as a temperature of the secondary battery. Accordingly, it is possible to control charging of the secondary battery according to the temperature thereof.
Patent Reference 1 has disclosed such a conventional battery monitoring IC. The conventional battery monitoring IC disclosed in Patent Reference 1 is formed of a micro computer (MPU: Micro Processing Unit) having a standard power source disposed therein for generating a standard voltage to be used for an analog-digital conversion (A/D). The MPU is configured to be driven by an external input power source. Further, the MPU is configured to receive a temperature detection voltage V1 from a thermistor connected to a voltage dividing resistor and a reference voltage V2 obtained through dividing a power source voltage of the external input power source with the voltage dividing resistor. Further, the MPU is configured to convert the temperature detection voltage V1 to a voltage ADV1 and the reference voltage V2 to a voltage ADV2 through the A/D conversion.
Patent Reference 1: Japanese Patent Publication No. 2008-111761
In the conventional battery monitoring IC disclosed in Patent Reference 1, a comparison circuit calculates a division result of the voltage ADV1 and the voltage ADV2 (ADV1/ADV2), which is represented by a resistivity value of the thermistor and a resistivity value of the voltage dividing resistor. Accordingly, when the MPU calculates the division result with the resistivity value of the thermistor, it is possible to obtain the resistivity value of the thermistor. In the next step, after the MPU converts the resistivity value of the thermistor to the temperature, it is possible to detect the temperature. The conventional battery monitoring IC disclosed in Patent Reference 1 has such a configuration described above, so that it is not necessary to stabilize the external input power source.
Patent Reference 2 has disclosed a conventional temperature measurement circuit. The conventional temperature measurement circuit disclosed in Patent Reference 2 is formed of a power source circuit, a microcomputer, and a temperature sensitive resistor element circuit. The temperature sensitive resistor element circuit is formed of a series circuit of a thermistor and a voltage dividing resistor. The power source circuit applies a power source voltage as an input voltage to the thermistor. The input voltage and an output voltage as a voltage at a connection point between the thermistor and the voltage dividing resistor are input into the microcomputer, so that an A/D converter converts the input voltage and the output voltage into digital values.
Patent Reference 2: Japanese Patent Publication No. 2005-274372
In the conventional temperature measurement circuit disclosed in Patent Reference 2, the micro computer stores a table indicating a relationship between the input voltage and the output voltage thus digitally converted, and a temperature detection data. Accordingly, when the microcomputer refers to the table, it is possible to measure the temperature. When the conventional temperature measurement circuit has the configuration disclosed in Patent Reference 2, it is possible to measure the temperature compensated according to a change in the power source voltage.
In the conventional battery monitoring IC disclosed in Patent Reference 1, and the conventional temperature measurement circuit disclosed in Patent Reference 2, the main configuration is formed of the semiconductor device having the calculation function, the comparison function, and the like realized with the MPU, the microcomputer, and the like. Accordingly, the semiconductor device has the function of measuring a temperature as a supplemental function.
In other words, according to the conventional battery monitoring IC disclosed in Patent Reference 1 and the conventional temperature measurement circuit disclosed in Patent Reference 2, the conventional semiconductor device is capable of performing a calculation as the primary function. In the semiconductor device, it is possible to easily perform a relatively complex calculation. Further, it is possible to easily store a table with a large capacity according to various conditions. As a result, it is possible to easily achieve the temperature measurement circuit capable of suppressing an influence of a variance in the power source voltage.
On the other hand, when the semiconductor device has only a limited function such as a function of monitoring a battery, it is necessary to minimize a circuit scale as much as possible. Accordingly, it is difficult to provide a calculation circuit, a comparison circuit, or a memory with a large capacity.
Further, when the semiconductor device includes the A/D conversion circuit, the A/D conversion circuit tends to increase a circuit scale thereof for accurately measuring a temperature and a voltage. Accordingly, an area of the A/D conversion circuit to be disposed in the semiconductor device tends to increase as well. For the reason, it is not desirable to dispose a plurality of A/D conversion circuits in the conventional semiconductor device as disclosed in Patent Reference 1. In the conventional semiconductor device, however, it is still necessary to secure a certain accuracy of the temperature measurement. In particular, it is necessary to reduce a measurement error of a temperature due to the variance in the power source voltage applied to the thermistor as much as possible.
As a summary, when the conventional semiconductor device does not have the calculation function like those of the conventional semiconductor devices disclosed in Patent References 1 and 2, such a conventional semiconductor device is configured to be limited to the simple function of monitoring the battery, so that the circuit scale and the cost thereof are restricted. Accordingly, in the conventional semiconductor device with the simple function, it is difficult to obtain the temperature measurement circuit capable of achieving accuracy comparable to that of the conventional semiconductor devices disclosed in Patent References 1 and 2.
In view of the problems of the conventional semiconductor devices described above, a subject of the present invention is to provide a semiconductor device having a temperature measurement circuit with a simple configuration capable of measuring a temperature with high accuracy. Another object of the present invention is to provide a battery monitoring system using the semiconductor device, and a method of monitoring a battery using the semiconductor device.
Further objects and advantages of the invention will be apparent from the following description of the invention.